1. Field of the Invention
This invention relates to a method of continuously separating a molten salt by-product phase from a molten uranium or molten uranium alloy product phase by use of a barrier which will pass molten salt but retain molten metal. Application of the method is possible in such activities as (a) production of uranium from uranium fluoride; (b) separation of uranium from solid mixtures of uranium and salt; (c) preparation of uranium alloys; (d) direct casting, i.e., without remelting; (e) recovery and cleaning of uranium scrap for recycle; and (f) molten by-product decontamination.
2. Description of the Related Art
The opposite separation, i.e., passing molten uranium or molten uranium alloy and retaining molten salt, was employed in earlier patents by G. R. B. Elliott: U.S. Pat. Nos. 4,534,792; 4,552,588; 4,564,507; 4,591,382; 4,636,250; Canadian 1 241 201; 1 241 202; and European application (accepted) 85302664.9. All the earlier claims are tied to the use of a molten uranium trap, which trap is based on the high density of uranium relative to that of the molten salt. That earlier separation uses a very different concept from that of the present invention, which is primarily tied to the highly dissimilar interfacial behaviors of the molten phases in their interactions with ceramics and other third phase materials.
None of the earlier Elliott patents are in commercial use yet, although we have used the concepts in operations at our pilot plant.
Commercial large scale uranium production is based on batch reductions, almost exclusively by the Ames process, which is described below. In the U.S. that process is used by the two still active commercial producers of the uranium, and it has been used commercially by at least six other producers, private or governmental.
The operational form of the Ames process is still used basically as it was developed in World War II under wartime pressures and concerns. Heated uranium fluoride (usually the tetrafluoride) with chipped magnesium reacts at temperatures rising to around 1500.degree. C. and pressures of magnesium vapor of hundreds of pounds per square inch. During the reaction radioactive reagents and products escape to the air and have repeatedly escaped to the outside environment also. Next, large amounts of molten magnesium fluoride and molten uranium (as much as 4500 pounds per batch) are formed, caus-safety problems in some cases, at least. These molten phases are frozen and cooled to room temperature where they are manually broken apart. The uranium product ("derby") must be remelted before it is cast, and alloying elements can also be added. The by-product comprising primarily magnesium fluoride is radioactive enough to cause serious environmental problems in disposal, and it is not suitable for recycle.
Now people justifiably have demanded safety and environmental protection: Of the eight producers just mentioned, two dropped out before environmental concerns became dominant, and four have shut down because of environmental problems connected with the Ames process. These closures are in spite of what has been recognized as great importance of uranium production for National security.
The Ames process, therefore, is demonstrated to be seriously flawed for current usage. The basic problem has been the absence, until the recent Elliott inventions, of any means to carry out the reductions at atmospheric pressure and continuously.
The present invention is complementary to the earlier Elliott inventions noted. Although some of the activities could be done with either continuous separations method alone, others need, or perform better with, both separations performed simultaneously, as discussed in the summary.